1. Field of the Invention
The present invention relates to a light guide plate and a surface light source unit using the same, and especially to a light guide plate providing highly uniform illumination and high brightness.
2. Description of Prior Art
Recently, liquid crystal display devices have undergone remarkable improvements, and their market has been steadily growing. These devices save installation space by virtue of their slimness, and they can also save on power consumption.
Liquid crystal displays commonly use a surface light source unit to provide illumination. The surface light source unit includes a light guide plate having a uniform thickness or being wedge-shaped. The light guide plate distributes light from a substantially linear source such as a cold cathode fluorescent lamp (CCFL), in order to provide substantially even illumination to the LCD.
FIG. 4 shows a conventional surface light source unit 1, which comprises a light source 11, a light guide plate 13 adjacent to the light source 11, a reflective plate 12, a diffusing plate 14 and a prism plate 15. The reflective plate 12 and the diffusing plate 14 are disposed under and on top of the light guide plate 13, respectively. The prism plate 15 is disposed on the diffusing plate 14, and has a plurality of prisms 151. Light beams from the light source 11 enter the light guide plate 13 through a light incidence surface 131 thereof. Some of the light beams are diffused and reflected by a bottom surface 133 of the light guide plate 13, and emit from an emission surface 132 of the light guide plate 13. Other light beams emit from the bottom surface 133, are reflected by the reflective plate 12 back into the light guide plate 13, and then emit from the emission surface 132. The light beams emitted from the emission surface 132 are diffused by the diffusing plate 14, and then enter the prism plate 15. The prism plate 15 improves the directivity of the light beams, so that the surface light source unit 1 has a predetermined directivity.
However, the surface light source unit 1 has an unduly large number of parts. This makes assembly of the surface light source unit 1 complicated, and inflates costs.
FIG. 5 shows another conventional surface light source unit 2, which comprises a light source 21, a light guide plate 20 and a reflective plate 23. The light guide plate 22 comprises a light incidence surface 201, a bottom surface 203 having a plurality of diffusion dots 221 formed thereon, and an emission surface 202 having a plurality of parallel prisms 222 formed thereon. The prisms 222 are arranged on the emission surface 202 contiguously, and are parallel to the light incidence surface 201. However, the light intensity distribution in the light guide plate 22 is not uniform. Accordingly, the surface light source unit 2 cannot provide uniform illumination.
It is desired to provide a light guide plate that solves the above-mentioned problems.